Atoms hollowed by laser form novel plasma

EuroPhotonicsJun 2013
A highly unusual plasma composed of hollow atoms has been created using one of the world’s most powerful lasers. The surprising result shows that a little-explored region of physics is now accessible through the unprecedented intensities being reached at some laser facilities.

A hollow atom occurs when an electron buried in an atom is removed – usually by being hit by another electron – creating a hole. This process creates plasma, a form of ionized gas. An x-ray is released when the hole is filled.

A highly unusual plasma composed of hollow atoms has been created using one of the world’s most powerful lasers – the Vulcan petawatt laser. Courtesy of the Central Laser Facility.
The process normally involves removing electrons from the outer shells of atoms first and working inward. “These x-rays empty the atoms from the inside out – a most extraordinary observation and one that suggests the physics of these interactions is likely to change as lasers become more powerful,” said principal investigator Dr. Nigel Woolsey of York Plasma Institute at the University of York. The work, led by scientists from the University of York and the Russian Academy of Sciences’ Joint Institute for High Temperatures, shows that it is possible to remove the two most deeply bound electrons from atoms. The experiment, carried out using the Vulcan petawatt laser at the Central Laser Facility at Rutherford Appleton Laboratory, could advance understanding of fusion energy generation, which employs plasmas hotter than the sun’s core and which is a potential supply of safe, limitless energy.

“At such extraordinary intensities, electrons move at close to the speed of light, and as they move, they create perhaps the most intense x-rays ever observed on Earth,” Woolsey said.

Analysis and theoretical work, led by Los Alamos National Laboratory (LANL) in the US and Osaka University in Japan, showed the mechanism for hollow atom generation was not because of the collision of electrons or driven by the laser photons, but rather was driven by the resulting radiation field from the interaction.

“Future experiments are likely to show yet more dramatic effects, which will have substantial implications for diverse fields such as laboratory-based astrophysics,” said co-author Dr. Alexei Zhidkov of Osaka University.